Actuator for objective lenses

ABSTRACT

A resilient support member  5  is provided between a lens holder  2  and a base member  4  to resiliently support the lens retainer  2  with respect to the base member  4 . A pair of auxiliary damping members  10   a  and  10   b  extend along the length of the resilient support member  5 , and a viscoelastic material piece  11  is provided between the two auxiliary damping members so as to connect them to each other. Various modes of connection can be achieved, and the freedom in the tuning of the damping effect is increased for reducing spurious resonant vibrations so that an adequate damping effect can be achieved. Because the part to which the viscoelastic material is to be applied is placed in a wide space remote from the lens retainer and the base member, the work of applying the viscoelastic material is simplified.

TECHNICAL FIELD

The present invention relates to an object lens actuator for use inoptical disk devices and other applications.

BACKGROUND OF THE INVENTION

As a support structure for an object lens actuator for optical diskdevices, it is conventionally known to resiliently support a lens holderretaining an object lens with a wire member extending from a base memberas disclosed in Japanese UM registration No. 2521564. In thisconventional arrangement, a piece of viscoelastic material is used fordamping the resonant vibrations of the wire member and other parasiticvibrations.

However, this conventional arrangement has the following problems.

1) Because the viscoelastic material piece is placed adjacent to themounting part of the wire member, the deformation of the spring membercaused by the movement of the holder is relatively small. Therefore, theshear force acting between the wall of the space surrounding the freeend of the wire member and the spring member is so small that anadequate damping effect may not be produced.

2) Because of the need to fill the viscoelastic material into the spacesurrounding the mounting portion of the wire member, the work efficiencyis low.

3) Because the viscoelastic material is required to be filled into thespace which is larger than the outer profile of the wire member, whenthe viscoelastic material is required to be cured by ultravioletradiation, the space is required to be formed with transparent resinmaterial (transmitting ultraviolet radiation) so that there is arestriction on the selection of the resin material.

SUMMARY OF THE INVENTION

To eliminate such problems of the prior art, and achieve an adequatedamping effect while improving the work efficiency in forming thedamping means, the present invention provides an object lens actuator,comprising a lens holder retaining an object lens, a resilient supportmember extending from a base member toward the lens holder forresiliently supporting the lens holder with respect to the base member,and drive means for actuating the lens holder in focusing and trackingdirections, further comprising: an auxiliary damping member extendingfrom at least one of the lens holder and the base member along thelength of the resilient support member; and damper means providedbetween the resilient support member and the auxiliary damping member orbetween two of the auxiliary damping members; or further comprising apair of auxiliary damping members extending from the lens holder andbase member, respectively, along the length of the resilient supportmember; and damper means provided between the opposing ends of theauxiliary damping member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an essential part of an optical headembodying the present invention;

FIG. 2 is a plan view of an essential part of the optical head of FIG.1;

FIG. 3 is a view showing the resilient support member and the auxiliarydamping members embodying the present invention:

FIG. 4 is an enlarged view of an essential part similar to FIG. 3showing a second embodiment of the present invention;

FIG. 5 is an enlarged view of an essential part similar to FIG. 3showing a third embodiment of the present invention;

FIG. 6 is an enlarged view of an essential part similar to FIG. 3showing a fourth embodiment of the present invention; and

FIG. 7 is an enlarged view of an essential part similar to FIG. 3showing a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective view of an essential part of an optical head foroptical disk devices and magneto-optical disk devices embodying thepresent invention, and FIG. 2 is a plan view of the same. This opticalhead comprises a block-shaped lens holder 2 adapted to retain an objectlens 1, and four band-shaped resilient support members 5 which, forresiliently supporting the lens holder 2 with respect to a wall-likebase member 4 standing upright from a mounting plate 3, extend from thebase member 4 substantially in parallel with the mounting plate 3, oneabove the other on either side of the lens holder 2, and attached tointermediate parts of the lens holder 2 on either side of the lensholder 2 at their free ends.

The object lens 1 is mounted to an end portion of the lens holder 2remote from the base member 4 with its optical axial line directedperpendicularly to the major surface of the mounting plate 3. Themounting plate 3 is actuated by a drive device provided in a device mainbody not shown in the drawing for a rough positioning action.

An intermediate part of the lens holder 2 is provided with a throughhole 2 a extending substantially perpendicularly to the extendingdirection of the resilient support members 5. A rectangular annularfocusing coil 6 is fitted in a part of this through hole 2 a adjacent tothe base member 4 and a pair of tracking coils 7 are attached to thefront face (facing the object lens 1) of the focusing coil 6 one next tothe other. Magnet units 8 and 9 each consisting of a yoke and apermanent magnet are attached to the mounting plate 3 in an uprightorientation. One of the magnet units 8 is passed into the focusing coil6. The other magnet unit 9 is passed into the part of the through hole 2a defining a certain area offset from the focusing coil 6 toward theside of the object lens 1, and faces the tracking coils 7. The focusingcoil 6 and tracking coils 7 form the drive means jointly with the magnetunits 8 and 9.

The resilient support members 5 are each formed by cutting out a singlesheet spring member along arcuate paths as shown in FIG. 3, and, in itsmounted state, presents a convex profile in the tracking direction whileextending in parallel with the major surface of the mounting plate 3.The resilient support members 5 are each provided with mounting pieces 5a at longitudinal ends thereof for attachment to the lens holder 2 andthe base member 4, respectively A pair of auxiliary damping members 10 aand 10 b are cut out from the same sheet spring member as the resilientsupport member 5, and extend from the mounting pieces 5 a toward eachother and along the length of the resilient support member 5.

In the embodiment shown in FIGS. 1 and 2, the free ends of the twoauxiliary damping members 10 a and 10 b oppose each other, and aviscoelastic material piece 11 is provided between the free ends so asto connect the free ends to each other with the viscoelastic materialpiece 11. According to this embodiment, because the resilient supportmember 5 and the auxiliary damping members 10 a and 10 b are formedintegrally to one another, it is possible to form both the part forsupporting the lens holder 2 so as to be moveable in the focusing andtracking directions, and the auxiliary function for damping aspring-mass system with a single member.

When the object lens actuator is actuated in the focusing or trackingdirection, a relative displacement is produced between the auxiliarydamping member 10 a on the side of the lens holder 2 and the auxiliarydamping member 10 b on the side of the base member 4, and theviscoelastic material piece 11 produces a damping effect owing to theshear force which is produced in the viscoelastic material piece 11extending between the free ends.

Because the viscoelastic material piece 11 is provided in anintermediate part which is remote from both the lens holder 2 and thebase member 4, the work of applying the viscoelastic material can beconducted in a relatively wide open space as opposed to the enclosedspace of the prior art, and the work efficiency can be improved. Also,when the viscoelastic material piece 11 consists of a material which isrequired to be cured by ultraviolet radiation, because there is nothingto obstruct ultraviolet radiation, the work efficiency of ultravioletradiation can be improved, and the curing process can be conducted in astable manner.

In the embodiment described above, the resilient support member 5 forsupporting the lens holder in the focusing and tracking directions wascurved at a certain curvature so that the axial (longitudinal)compliance of the resilient support member 5 may be increased althoughthey may simply extend straight without departing from the spirit of thepresent invention. As a result, spurious resonant frequencies ofpitching, yawing and other motions of the spring-mass system are shiftedtoward lower frequency ranges as opposed to the case of a resilientsupport member having no such curvature. In general, the damping effectof a damping material depends on the frequency, and diminishes as thefrequency gets higher. Therefore, by providing a curvature to theresilient support member 5 and thereby lowering the spurious resonantfrequencies of the spring-mass system, the damping effect can beenhanced.

The present invention is not limited by the foregoing embodiment, butmay be implemented in various other different arrangements. Some of suchpossible embodiments of the present invention are described in thefollowing.

FIGS. 4 and 5 are views similar to FIG. 3 showing essential parts of theresilient support member 5 and the auxiliary damping members 10 a and 10b. In the embodiment illustrated in FIG. 4, the viscoelastic materialpiece 11 not only connects the free ends of the two auxiliary dampingmembers 10 a and 10 b, but also connects a corresponding part of theresilient support member 5 to the auxiliary damping members 10 a and 10b. In the embodiment illustrated in FIG. 5, instead of directlyconnecting the free ends of the auxiliary damping members 10 a and 10 bwith the viscoelastic material piece 11, the free ends of the auxiliarydamping members 10 a and 10 b are individually connected to the opposingparts of the resilient support member 5 with the viscoelastic materialpiece 11. These illustrated embodiments allow the damping effect to befreely tuned, and increase the freedom of design so that the device maybe readily adapted to each particular need.

In the embodiment illustrated in FIG. 6, the resilient support member 5is provided with a projection 12 which fits into a gap defined betweenthe opposing free ends of the auxiliary damping members 10 a and 10 b,and the projection 12 is individually connected to the free ends of theauxiliary damping members 10 a and 10 b with two separate pieces of theviscoelastic material 11. This increases the roll rigidity of the lensholder 2, and contributes to the reduction of spurious resonantvibrations.

In the embodiment illustrated in FIG. 7, the opposing free ends of theauxiliary damping members 10 a and 10 b are provided with mutuallycomplementary step-shaped edges so that the step-shaped free endsinterdigitate. The viscoelastic material piece 11 extends between thestep-shaped free ends.

The embodiments illustrated in FIGS. 4 to 7 provide similar advantagesas the first embodiment. In the embodiments illustrated in FIGS. 4 to 6,the auxiliary damping members extended from both the lens holder 2 andthe base member 4 in a pair, but the auxiliary damping member may alsoextend only from one of them or extend from both the lens holder 2 andthe base member 4 by different lengths. The viscoelastic material piece11 was provided only in a part of the entire length of the resilientsupport member in the above described embodiments, but may also beprovided over the entire length of the resilient support member.

The resilient support member 5 and the auxiliary damping members 10 aand 10 b were formed from the same blank, but may also be formed fromdifferent blanks. Even in the latter case, similar advantages can beobtained.

INDUSTRIAL APPLICABILITY

Because the damping member extends from one of the lens holder and thebase member and a damping material piece is provided between theresilient support member and the auxiliary damping member, or theauxiliary damping members extend from the lens holder and the basemember in a pair, respectively, and a damping material piece is providedbetween the free ends of the auxiliary damping members, the viscoelasticmaterial can be applied in various different ways. Therefore, thedamping effect can be freely tuned, and the freedom of design isincrease so that an adequate damping effect can be achieved. Also,because the work of applying the viscoelastic material can be conductedin a relatively wide open space remote from both the lens holder 2 andthe base member 4, the work efficiency can be improved.

What is claimed is:
 1. An object lens actuator, comprising a lens holderretaining an object lens, a resilient support member extending from abase member toward the lens holder for resiliently supporting the lensholder with respect to the base member, and drive means for actuatingthe lens holder in focusing and tracking directions, further comprising:a pair of auxiliary damping members extending from the lens holder andthe base member, respectively, along the length of the resilient supportmember so as to oppose each other and define a gap between them; anddamper means provided between the resilient support member and theauxiliary damping members.
 2. An object lens actuator according to claim1, wherein the resilient support member and the auxiliary dampingmembers are formed integrally to each other.
 3. An object lens actuatoraccording to claim 1, wherein the resilient support member curves so asto face a convex part thereof in the tracking direction.
 4. An objectlens actuator according to claim 1, wherein the damper means connectsthe opposing ends of the auxiliary damping members.
 5. An object lensactuator according to claim 1, wherein the resilient support member isprovided with a projection which extends into the gap between theopposing ends of the auxiliary damping members, and the damper means isprovided between the projection and the free end of each of theauxiliary damping members.
 6. An object lens actuator, comprising a lensholder retaining an object lens, a resilient support member extendingfrom a base member toward the lens holder for resiliently supporting thelens holder with respect to the base member, and drive means foractuating the lens holder in focusing and tracking directions, furthercomprising: a pair of auxiliary damping members extending from the lensholder and the base member, respectively, along the length of theresilient support member so as to oppose each other and define a gapbetween them; and damper means provided between the opposing ends of theauxiliary damping members.
 7. An object lens actuator according to claim6, wherein the resilient support member and the auxiliary dampingmembers are formed integrally to each other.
 8. An object lens actuatoraccording to claim 6, wherein the resilient support member curves so asto face a convex part thereof in the tracking direction.
 9. An objectlens actuator according to claim 6, wherein the opposing free ends ofthe auxiliary damping members are provided with mutually complementarystepshaped edges.
 10. An object lens actuator according to claim 6,wherein the opposing free ends of the auxiliary damping members opposeeach other adjacent to a middle point between the lens holder and thebase member.
 11. An object lens actuator, comprising a lens holderretaining an object lens, a resilient support member extending from abase member toward the lens holder for resiliently supporting the lensholder with respect to the base member, and drive means for actuatingthe lens holder in focusing and tracking directions, further comprising:an auxiliary damping member extending from at least one of the lensholder and the base member along the length of the resilient supportmember; and damper means provided between the resilient support memberand the auxiliary damping member or between two of the auxiliary dampingmembers; the resilient support member curving so as to face a convexpart thereof in the tracking direction.